We actually don't know that. Korea has avoided it, for now. People were saying the same thing about Japan and Singapore. But both had outbreaks that flared u

We actually don't know that. Korea has avoided it, for now. People were saying the same thing about Japan and Singapore. But both had outbreaks that flared up. They'll have to keep doing what is working until a vaccine occurs or the disease dies. But even if its possible to prevent an massive outbreak that doesn't mean its possible to undo a massive outbreak. Korea has prevented large scale community spread by testing and tracing. That has been a successful and preventing an outbreak. But nobody has ever successfully used it to remove a virus from a population after it was already widely in the population.